The application provides a process for depositing a minimal load of an electrocatalyst (preferably comprising platinum) onto a support, preferably a support capable of use as a fuel cell electrode (most preferably carbon cloth). While maximizing the catalytic activity of the catalyst. The application also is directed to products comprising novel electrocatalytic coatings comprising rod-shaped structures.
A fuel cell is an electrochemical device in which electrical energy is generated by chemical reaction without altering the basic components of the fuel cellxe2x80x94that is, the electrodes and the electrolyte. Fuel cells combine hydrogen and oxygen without combustion to form water and to produce direct current electric power. The process can be described as electrolysis in reverse. The fuel cell is unique in that it converts chemical energy continuously into electrical energy without an intermediate conversion to heat energy.
Fuel cells have been pursued as a source of power for transportation because of their high energy efficiency (unmatched by heat engine cycles), their potential for fuel flexibility, and their extremely low emissions. Fuel cells have potential for stationary and vehicular power applications; however, the commercial viability of fuel cells for power generation in stationary and transportation applications depends upon solving a number of manufacturing, cost, and durability problems.
One of the most important problems is the cost of the proton exchange catalyst for the fuel cell. Some of the most efficient catalysts for low temperature fuel cells are noble metals, such as platinum, which are very expensive. Some have estimated that the total cost of such catalysts is approximately 80% of the total cost of manufacturing a low-temperature fuel cell.
In a typical process, an amount of a desired noble metal catalyst of from about 0.5-4 mg/cm2 is applied to a fuel cell electrode in the form of an ink, or using complex chemical procedures. Unfortunately, such methods require the application of a relatively large load of noble metal catalyst in order to produce a fuel cell electrode with the desired level of electrocatalytic activity, particularly for low temperature applications. The expense of such catalysts makes it imperative to reduce the amount, or loading, of catalyst required for the fuel cell. This requires an efficient method for applying the catalyst.
In recent years, a number of deposition methods, including rolling/spraying, solution casting/hot pressing, and electrochemical catalyzation, have been developed for the production of Pt catalyst layers for proton exchange membrane (PEM) fuel cells. Although thin sputtered Pt coatings deposited on carbon cloth can measurably improve fuel cell performance, this approach generally is not considered to be viable for large area deposition or as a stand alone treatment for applying platinum. Continuing challenges remain in the development of scalable methods for the production of large-area ( greater than 300 cm2), high performance ( greater than 1 A/cm2 at 0.6 V) fuel cell electrodes with low Pt loadings ( less than 0.3 mg/cm2).
The present invention provides a method for depositing onto a support a vaporizable composition comprising a catalytic component. The method comprises converting the vaporizable composition into a vapor, and depositing the vapor onto the support in an amount sufficient to produce a concentration of the catalytic component adapted to produce a catalytically effective coating on the support. The invention also is directed to electrodes produced by the method, and to electrodes comprising a support comprising a deposit disposed thereon which comprises a catalytically effective load of an electrocatalyst comprising an electrocatalytic active area at least in part comprising rod-shaped structures.